1. Field of the Invention
The present invention relates to a circuit breaker that may typically be provided halfway on power cables in an electric vehicle.
2. Description of the Related Art
Certain models of electric vehicles have a circuit breaker provided halfway on power cables so that they can be disconnected if necessary as in maintenance. A prior art example of such circuit breaker is described in Unexamined Published Japanese Patent Application (kokai) No. 223439/1997. As shown in FIG. 10, the circuit breaker which is generally indicated by a comprises a casing b and two cylindrical fixed electrodes c and d erected within the casing b to provide a bipolar structure. One fixed electrode c is connected to a terminal metal plate f pressed against an electric cable e whereas the other fixed electrode d is connected to an end of a fuse i via a bus bar h. The other end of the fuse i is connected to a terminal metal plate g pressed against an electric cable e.
A moving electrode j having a handle o can be brought into or out of engagement with the fixed electrodes c and d. The combination of these electrodes constitutes a breaker switch p which is connected in series with the fuse i between the electric cables. The moving electrode j of the breaker switch p has contacts k and m that establish communication via a communicating portion n. The contacts k and m are brought into or out of engagement with the fixed electrodes c and d to establish or break continuity between the electric cables e.
Electric vehicles today are required to use smaller and lighter parts, among which the circuit breaker a is by no means an exception. A problem with this circuit breaker is that its minimum size is determined by the bipolar structure of the fixed electrodes c and d and the demand for further reduction in size and weight cannot be met.
As another problem, in order to bring the moving electrode j into engagement with the fixed electrodes c and d, the two contacts k and m need have registry with the respective fixed electrodes c and d but this involves a cumbersome operation. If the contacts and the fixed electrodes are installed in positions offset from the exact correspondence, the pressure required to insert the moving electrode j increases, making it difficult to bring this electrode into or out of engagement with the fixed electrodes.
The present invention has been accomplished under these circumstances and has as an object providing a circuit breaker that is made smaller and lighter and which permits ease in bringing the moving electrode into or out of engagement with the fixed electrodes.
To achieve the above object, according to a first aspect of the invention, there is provided a circuit breaker comprising a pair of fixed electrodes, a moving electrode that is brought into or out of engagement with the fixed electrode pair to connect or disconnect the fixed electrodes, and a housing of the moving electrode that is made of an insulating resin, said moving electrode having in integral combination with retainer pieces that are retained in the housing, a contact lug that either contacts or detaches from the fixed electrodes, and a narrow-width joint that joins the retainer pieces and the contact lug.
According to a second aspect of the invention, the retainer pieces form a tubular shape that surrounds the contact lug.
According to a third aspect of the invention, the contact lug is split in the distal end portion by means of a slit extending from the distal end toward the basal end.
According to a fourth aspect of the invention, the fixed electrodes are each provided with an elastic lug formed by bending the free end in a U shape to be parallel with the direction in which said moving electrode is inserted.
In the first aspect of the invention, the pair of fixed electrodes have a unipolar structure that is created by arranging two electrodes to face each other. Compared to fixed electrodes arranged to have a bipolar structure, the unipolar structure requires a smaller space of installation and a smaller and lighter circuit breaker can be realized. The fixed electrodes of a unipolar structure have the additional advantage of reducing the likelihood for the occurrence of a positional offset between the fixed electrode pair and the moving electrode, thus providing ease in bringing the moving electrode into or out of engagement with the fixed electrodes. As a further advantage, the moving electrode is contained in a housing made of an insulating resin, so safety is assured when bringing it into or out engagement with the fixed electrodes.
Since the moving electrode is contained in the housing, one may suspect that the positioning action of the housing could introduce, rather than eliminate, a positional offset from the fixed electrodes. But this will not happen in the present invention; the contact lug of the moving electrode that contacts the fixed electrode pair and the retainer piece retained in the housing are joined via the narrow-width joint, and upon flexing to deform, the joint absorbs any positional offset to ensure that no galling force will be exerted upon the moving electrode or the fixed electrodes. This provides greater ease in the process of bringing the moving electrode into or out of engagement with the fixed electrodes.
In the second aspect of the invention, since the retainer pieces of the moving electrode are formed in a tubular shape that surrounds the contact lug, there is no possibility for the contact lug to deform by bumping against a foreign object or to be damaged in the manufacturing process at the step of installing the moving electrode on the housing.
In the third aspect of the invention, since the distal end portion of the contact lug of the moving electrode is split into two parts by means of a slit, the moving electrode, when brought into engagement with the fixed electrodes, has better fit to assure stable contact with the latter.
In the fourth aspect of the invention, since the fixed electrodes are each provided with the elastic lug, they can have more stable contact with the contact lug of the moving electrode.